A liquid crystal display (LCD) is one of the most widely used flat panel displays. An LCD includes two panels provided with field-generating electrodes, and a liquid crystal (LC) layer interposed therebetween. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer, which determines orientations of LC molecules in the LC layer to adjust polarization of incident light.
An LCD may have switching elements to switch voltages of pixels arranged in a matrix form. An LCD can display various images since pixel voltages are individually switched. An LCD having switching elements to switch pixel voltages individually is called an active matrix LCD.
Thin film transistors or thin film diodes may be used as the switching elements. When thin film diodes are applied, MIM diodes can be used.
A MIM diode has two metal layers and one insulating layer interposed between the metal layers, and a thickness capable of being measured in micrometers. A MIM diode may act as a switch due to electrical non-linearity of the insulating layer. A MIM diode has two terminals, and as a result, the manufacturing process of the MIM diode is simpler than that of the thin film transistor having three terminals. Accordingly, MIM diodes can be manufactured at a lower cost than thin film transistors.
However, when diodes are used as switching elements, the uniformity of image quality and contrast ratio may be degraded due to asymmetry of an applied voltage with respect to the polarity.
In response to the asymmetry, a dual select diode (DSD) panel has been developed. A DSD panel includes two diodes that are symmetrically connected to a pixel electrode and are driven by applying voltages of opposite polarities.
A DSD LCD shows improved image quality, contrast ratio, gray scale uniformity, and response speed by applying voltages having opposite polarities to two diodes that are connected to the same pixel electrode. Accordingly, a DSD type LCD can display images with high resolution like that of an LCD using thin film transistors.
A thin film diode array panel of a conventional DSD LCD has transmission electrodes made of a transparent conductor such as indium tin oxide (ITO) formed on a substrate as a bottom layer, and signal lines made of a metal and formed on the other layers as a top layer.